A Passive Optical Network (PON) based access systems such as those specified in the International Telecommunications Union (ITU) Gigabit Passive Optical Network (GPON) standard (G.984) and ITU Broadband Passive Optical Network (BPON) standard (G.983) requires a preamble to allow clock recovery on an upstream signal.
Currently, there exists a tradeoff between how quickly a Clock Phase Aligner (CPA) or Clock Data Recovery (CDR) device can recover the correct clock phase from the incoming data stream and the amount of power consumed by the device. To reduce power consumption, longer preambles are employed. The primary advantage of MAC assisted clock recovery is a reduction in preamble which decreases overhead and therefore increases the percentage of the upstream bandwidth that is available to carry traffic.
Each Optical Network Unit (ONU) on the PON has a nearly constant phase relationship between its data stream and the local reference clock on the Optical Line Termination (OLT) that remains essentially constant over short to medium periods of time. The phase relationship changes as the fiber buried in the ground changes temperature. Since the ground temperature is fairly constant, and changes very slowly when it does change, the phase relationship between the ONU and LT remains constant for all practical purposes for periods of hours at a time. Therefore what is needed is a passive optical network media access controller assisted clock recovery that can take advantage of this constant phase relationship. More specifically, the present invention allows the PON Media Access Controller (MAC) to retain this constant phase relationship information any time a cell is received upstream, such as during ranging of a previous cell from a specific ONU which will be utilized to seed the CPA/CDR with a starting phase relationship value that will be extremely close to the optimized phase value thereby reducing the amount of time required for the CPA/CDR to acquire lock.